fix(attribution): one active attribution runtime per JVM

Statement listeners are JVM-wide. Starting attribution on another
instance now stops the previous runtime's listener and flusher, so
repeated server starts (tests, hot swaps) never pin old instances.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,7 @@ All notable changes are documented here. This project follows Keep a Changelog a
 ## [Unreleased]
 
 ### Fixed
+- Only one runtime attributes per JVM: starting attribution on a newer instance (a hot swap, or repeated server starts in tests) stops the previous one, so old instances are never pinned by a forgotten listener and flusher.
 - Each table has its own icon (the app icon is now `storage`), so nav entries are distinguishable and do not repeat icons used elsewhere.
 - Home tables keep at most four columns with plain headers (readable at every width): secondary facts such as calls and mean time, the session's query text, and a unit's kind and top table move into a second line of the first cell.
 

src/main/java/com/kingsrook/qbits/dbperformance/DbPerfRuntime.java

@@ -42,6 +42,12 @@ public class DbPerfRuntime implements QSupplementalInstanceMetaData
    private final DbPerfQBitConfig config;
    private AttributionFlusher attributionFlusher;
 
+   /////////////////////////////////////////////////////////////////////////////
+   // statement listeners are JVM-wide: only one runtime attributes at a time //
+   // (a newer instance, e.g. after a hot swap or in tests, replaces the old) //
+   /////////////////////////////////////////////////////////////////////////////
+   private static final AtomicReference<DbPerfRuntime> ACTIVE_ATTRIBUTION = new AtomicReference<>();
+
 
    /*******************************************************************************
     ** Runtime bound to a single host instance.
@@ -149,6 +155,11 @@ public class DbPerfRuntime implements QSupplementalInstanceMetaData
    {
       if(attributionFlusher == null && Boolean.TRUE.equals(config.getAttributionEnabled()))
       {
+         DbPerfRuntime previous = ACTIVE_ATTRIBUTION.getAndSet(this);
+         if(previous != null && previous != this)
+         {
+            previous.stopAttribution();
+         }
          attributionFlusher = new AttributionFlusher(this);
          attributionFlusher.start();
       }
@@ -160,6 +171,7 @@ public class DbPerfRuntime implements QSupplementalInstanceMetaData
     *******************************************************************************/
    public synchronized void stopAttribution()
    {
+      ACTIVE_ATTRIBUTION.compareAndSet(this, null);
       if(attributionFlusher != null)
       {
          attributionFlusher.close();

src/test/java/com/kingsrook/qbits/dbperformance/attribution/AttributionTest.java

@@ -569,6 +569,25 @@ class AttributionTest
    }
 
 
+   /*******************************************************************************
+    ** Only one runtime attributes per JVM: starting another stops the first, so
+    ** repeated server starts (tests, hot swaps) never pile up listeners.
+    *******************************************************************************/
+   @Test
+   void oneActiveRuntime() throws Exception
+   {
+      StatementExecutionListeners.unregister(listener);
+      runtime.startAttribution();
+      DbPerfRuntime other = new DbPerfRuntime(runtime.getInstance(), runtime.getConfig());
+      other.startAttribution();
+      runtime.stopAttribution();
+      assertThat(StatementExecutionListeners.isActive()).isTrue();
+      other.stopAttribution();
+      assertThat(StatementExecutionListeners.isActive()).isFalse();
+   }
+
+
+
    /*******************************************************************************
     ** Deliver a statement with exact counter values.
     *******************************************************************************/